The present invention relates to methods of recording a neural response following stimulation of neural tissue. More specifically, the present invention relates to methods for measuring and processing neural responses that minimize stimulus artifacts and system noise.
Modern neural stimulators have the capability of measuring the effectiveness of electrical stimulation of a nerve tissue. This involves delivering a stimulus to a nerve through a stimulating electrode and recording the electrical response, as the nerve depolarizes and repolarizes, using a recording electrode. Such recording and capturing of nerve electrical activity is termed neural response imaging (“NRI”).
Obtaining such a neural response (“NR”) is important clinically for determining whether stimulation of nerves is occurring at a given stimulus setting and also for determining optimal stimulation parameters for each electrode or electrode configuration.
High quality responses are often difficult to obtain because the neural recordings can be marred by the presence of stimulus artifacts, i.e., the neural recording records the voltage potential of the stimulus pulse rather than the desired NR signal. Another source of recording artifact is cross-talk between the recording circuit and the stimulation circuit. When the recording system is built into a small implantable system, such as an implantable cochlear stimulator or a spinal cord stimulator, the stimulation and recording circuits are necessarily placed very close to each other within the stimulator and, hence, cross-talk can develop between the two circuits.
Several conventional techniques exist for extracting NR, e.g., forward masking, alternating polarity and scaled template methods. These techniques, however, often leave large, residual artifacts, because they assume non-hysteresis and linearity of the system response.
Measurements in saline solution indicate that a large contributory factor to this residual artifact is due to non-linearities of the electrode-tissue interface at the stimulating electrode. This component may be either due to imperfections of the stimulating circuitry or to some poorly understood processes at the electrode-tissue interface.
Accordingly, what is needed is a method of recording and processing neural responses, that largely eliminates this residual artifact component.